Electric motor driven turbine pumps are customarily used in fuel systems of an automotive vehicle and the like. These pumps typically include an external sleeve which surrounds and holds together an internal housing adapted be submerged in a fuel supply tank with an inlet for drawing liquid fuel from the surrounding tank and an outlet for supplying fuel under pressure to an internal combustion engine of the vehicle. A shaft of the electric motor concentrically couples to and drives a pump impeller having an array of circumferentially spaced vanes disposed about the periphery of the impeller. An arcuate pumping channel carried by the housing substantially surrounds the impeller periphery and extends from an inlet port to an outlet port at opposite ends. Liquid fuel disposed in pockets defined between adjacent impeller vanes and the surrounding channel develops pressure through a vortex-like action induced by the three dimensional profile of the vanes and the rotation of the impeller.
Typically, impeller-type turbine fuel pumps have a stationary guide ring which strips fuel from the moving impeller vanes and diverts the fuel through an outlet port. The channel is located radially outward from the impeller vanes and radially inward from a substantial portion or trailing segment of the guide ring. In addition, the channel is located axially or laterally outward from both sides of the impeller at the circumferential array of vanes. In other words, the channel not only side-flanks or communicates axially with the impeller at the vane location from both sides, it also communicates with the vane pockets radially. A smaller portion, or striper segment of the guide ring, is disposed circumferentially between the inlet and outlet ports and is close to the impeller for striping the moving vanes of high pressure fuel, thereby, preventing the fuel at the outlet port from bypassing the fuel pump outlet and exiting back into the low pressure inlet port. Three examples of fuel pumps of this type are illustrated in U.S. Pat. No. 5,257,916 issued Nov. 2, 1993 to Tuckey, U.S. Pat. No. 6,068,456 issued May 30, 2000 to Tuckey et al. and U.S. Pat. No. 6,227,819 B1 issued May 8, 2001 to Gettel et al., each of which is assigned to the present assignee and is incorporated herein by reference.
A second type of turbine pump, such as that illustrated in U.S. Pat. No. 5,702,229 issued Dec. 30, 1997 to Moss et al. and incorporated herein by reference, has concentric dual circumferential arrays of vanes spaced radially apart by a mid-hoop or ring of the impeller, wherein both arrays communicate with a common channel. Similar to the first type of pump previously described, the outer array of vanes of this pump type project substantially radially outward from the periphery of the impeller toward a stationary guide ring. With this configuration, the fuel flows helically around the mid-hoop and through the channel. That is, the fuel flows about the mid-hoop as it is simultaneously circulating around the channel from an inlet to an outlet. Unfortunately, fuel flow cavitation within the pump, especially during hot fuel pumping conditions, continues to be a challenge.
A third type of turbine pump, as illustrated in U.S. Pat. No. 5,642,981 issued Jul. 1, 1997 to Kato et al. and incorporated herein by reference, is similar to the first example previously described, except that multiple pumps are arranged in series and powered by a common motor. Such pumps are better known as multi-stage pumps, or pumps having first and second stages, wherein the first stage (low pressure pump) feeds or flows fuel into a second stage (high pressure pump), thus being of a regenerative pump design. Unfortunately, multi-stage pump designs are expensive to manufacture and have an increased power consumption rate when compared to single stage designs.
Other types of turbine fuel pumps, such as that illustrated in U.S. Publication No. 2002/0021961 A1 published Feb. 21, 2002 to Pickelman et al. and U.S. Pat. No. 5,807,068 issued Sep. 15, 1998 to Dobler et al., both of which are incorporated herein by reference, do not utilize guide rings but instead have a peripheral hoop that is a unitary part of the impeller. The hoop engages the peripheral, radially outward distal ends of a circumferential array of impeller vanes. With this orientation, the impeller pockets only communicate with grooves of the channel in a lateral or axial direction. That is, communication between the impeller pockets and the channel is solely axial, or side-flanking. In contrast, the first and second types of turbine pumps have pockets that communicate with the channel in both an axial and a radial manner.
Despite the variety of turbine-type pumps and significant improvements in the design and construction of turbine fuel pumps on the market today, they are still somewhat inefficient. The efficiencies are generally between about 35%-45%, and when combined with a typical electric motor having an efficiency of about 45%-50%, the fuel pumps have an overall efficiency of between 16%-22%, in general. Higher flow and pressure requirements in the fuel pumping industry are exceeding the capabilities of conventional 36-39 mm diameter regenerative turbine fuel pumps. To increase fuel output and pressure, pumps must operate at higher speeds which aggravates cavitation concerns. Higher speed results in armature viscous drag (lost efficiency), noise and commutator wear. Maximum flow output under hot conditions is around 150 liters per hour for a conventional, single stage, turbine pump. Conventional alternatives to improve hot fuel flow are adding multi-pressure stages to the turbine pump, or oversizing the first stage of a two stage pump to accommodate a 30%-40% flow loss typical for regenerative pumps. However, such alternatives are costly and have an increase in power consumption, thus, which in turn decreases pumping efficiency.